To add a debit or credit card on an iPhone, open Wallet, tap the Plus (+) button and choose Debit or Credit Card. You can hold an eligible physical card near your iPhone or enter its details manually. Wallet may also show cards you've used previously so you can add them again. Follow the onscreen instructions to finish setting up the card.
The payment card needs to come from a participating issuer, and your bank or card provider may require another verification step before approving it for Apple Pay. If Wallet won't add the card, Apple recommends contacting the company behind the card for help.
This Plus menu is also where you can add other supported cards like transit passes, driver's licenses and ID cards. You may be able to easily add items in the From Apps on Your iPhone menu, too.
If you want to also use Apple Pay on an Apple Watch, iPad or Mac, adding a card to your iPhone doesn't automatically set it up everywhere. Those devices have their own Apple Pay setup steps.